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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

204

FERRO-TUNGSTEN

FERRO -TUNGSTEN

Ferro-tungsten is obtained by the direct reduction of natural wolframite
or scheelite with carbon in a crucible, or in the blast furnace or the electric
furnace, and serves for the preparation of tungsten steels.

Ferro-tungsten and steels with high tungsten contents (20%) are in-
soluble or difficultly soluble in acids, and to attack them it is necessary to
fuse with alkali. Their analysis includes :

1.  Determination of the Tungsten.—0-5-2 grams of the finely pow-
dered sample are fused with 10 parts of the mixture of sodium carbonate
and magnesia, as under Ferro-silicon, i 6, or I gram of the sample may be
fused \\ith 4—5 grams of sodium-potassium carbonate and 0-5 gram of
potassium nitrate.   In either case, the product is lixiviated with hot water,
sodium peroxide being added and the liquid boiled to destroy the excess
of this reagent, if the solution appears greenish owing to the presence of
manganates.   The liquid, which contains the tungsten as sodium tungstate,
is filtered into a 500 c.c. measuring flask and the residue repeatedly washed,
dried and again fused with sodium carbonate, the mass being lixiviated to
recover any small amount of tungsten which may have resisted the first
attack.

An aliquot part (50 or 100 c.c.) of the total solution is acidified with
hydrochloric acid, evaporated to dryness, heated at 135°, taken up again
in hydrochloric acid, etc., as described for the analysis of tungsten steel.

2.  Determination of the Carbon.—With products insoluble in acid,
direct oxidation in a current of oxygen must be employed (see Iron, i, b).

3.  Determination of the Silicon.—The procedure  employed with
ferro-silicon is followed, but since tungstic acid separates with the silica,,
the latter is treated with hydrofluoric acid and estimated by the loss in
weight (see Tungsten Steels).

4.  Determination of the Manganese.—This is carried out on the
residue remaining undissolved when the fused mass is lixiviated with water
(see Ferro-silicon, 3).

5.  Determination of the Phosphorus and Sulphur.—As in ferro-
silicon (see p. 196).

Crucible ferro-tungsten contains, on.the average, 25-30% W, 60-70% Fe
1-1-5% C, with traces of manganese, phosphorus, etc. ; that from the blast
furnace always contains considerable proportions of manganese (in some types,
up to 40%) and carbon (4-5%).

Ferro-tungsten obtained in the electric furnace usually has a high tungsten
content (80-90% W, 10-20% Fe, very small amounts of carbon, silicon and
manganese). Sometimes small quantities of calcium, magnesium, titanium,
aluminium, nickel, molybdenum, vanadium, etc., are also found.

The mean percentage compositions of some of the ferro-tungstens prepared
in the electric furnace are as follows (Bonini) :.oon as the liquid loses its yellow tint and becomes completely colour-